Comparing objects in Obj-C

Question

How does one compare objects in Objective-C?

Is it as simple as == ?

I want to check an array for an object and if it doesnt exist add it to the array other

Answer 1

Implement isEqual: and hash

Per the Apple documentation on NSObject you need to implement isEqual: and hash at a minimum. Below you'll find one way to implement object equality, of course how to implement hash enters the land of serious debate here on StackOverflow, but this will work. General rule - you need to define what constitutes object equality and for each unique object they should have a unique hash. It is best practice to add an object specific equality method as well, for example NSString has isEqualToString:.

- (BOOL)isEqual:(id)object
{
    BOOL result = NO;

    if ([object isKindOfClass:[self class]]) {
        CLPObject *otherObject = object;
        result = [self.name isEqualToString:[otherObject name]] &&
        [self.shortName isEqualToString:[otherObject shortName]] &&
        [self.identifier isEqualToString:[otherObject identifier]] &&
        self.boardingAllowed == [otherObject isBoardingAllowed];
    }

    return result;
}

- (NSUInteger)hash
{
    NSUInteger result = 1;
    NSUInteger prime = 31;

    result = prime * result + [_name hash];
    result = prime * result + [_shortName hash];
    result = prime * result + [_identifier hash];
    result = prime * result + _boardingAllowed;

    return result;
}